1. Field of the Invention
A utility vehicle guidance assembly for guiding a carriage, such as a lawnmower, over a plot of land, particularly a plot of uneven terrain.
2. Description of the Prior Art
A variety of guidance assemblies are known for guiding equipment such as lawnmowers over a lawn and many utilize a laser light beam in determining the position of the lawnmower on the lawn. A diode emits a beam of laser light in the generally horizontal direction and a support rotates the horizontal beam about a transverse axis which is upright relative to the carriage to move the horizontal beam radially between circumferentially spaced locating stations. The locating stations reflect the beam back to the carriage where it is processed to determine the position of the lawnmower and to control the guidance of the lawnmower over the terrain. An example of such an assembly is disclosed in U.S. Pat. No. 4,790,402 to Field et al., U.S. Pat. No. 4,918,607 to Wible, U.S. Pat. No. 5,142,788 to Willetts, U.S. Pat. No. 5,260,770 to Nakamura et al, and U.S. Pat. No. 5,426,584 to Kamimura et al.
Although such systems perform satisfactorily, there remains a constant desire to simplify and reduce the expense of such systems while retaining performance. A major performance criteria is to sweep the horizontal beam vertically sufficiently to reflect from locator stations that are of a minimum height as the lawnmower moves over very uneven or undulating terrain. Simultaneously with the vertical sweep of the horizontal beam it is necessary to maintain the vertical sweep in line with gravity, i.e., vertical, in order to obtain precise position data. This criterion requires an inexpensive and simplified system to compensate for misalignment of the upright axis of the lawnmower from vertical as the lawnmower moves over uneven terrain, i.e., non-horizontal as in undulating terrain.
The subject invention provides a method of guiding a carriage having an upright axis over a plot comprising the steps of emitting a vertical line of laser light defining a beam extending in the generally horizontal direction and generally radially from the upright axis, and rotating the horizontal beam about the upright axis to move the horizontal beam between circumferentially spaced locating stations. The method is characterized by moving the vertical line of light relative to the upright axis to compensate for misalignment of the upright axis from vertical in response to movement of the carriage over non-horizontal terrain.
In order to implement the method the invention includes a laser guidance assembly for a land vehicle having an upright axis comprising a diode device for emitting a vertical line of laser light, and a beam director for directing the vertical line of light in a horizontal beam and rotating the horizontal beam about a beam director axis to move the horizontal beam between circumferentially spaced locating stations. The assembly is characterized by an alignment mechanism for maintaining the vertical line of light in parallel alignment with gravity to compensate for misalignment of the upright axis of the vehicle from vertical to maintain the vertical line of laser light aligned with gravity as the vehicle moves over an uneven plot.
Accordingly, the invention provides a unique, simple and relatively inexpensive solution to the criteria of providing a wide variance in the vertical sweep of the horizontal beam in order to reflect the horizontal beam from relatively small locating stations notwithstanding a wide variance in the orientation of the upright axis of the vehicle due to movement over undulating terrain.